Supercritical fluid extraction of ten chloracetanilide pesticides and pyriminobac-methyl in crops: Comparison with the Japanese bulletin method

In Japan, the maximum residue limit and an analytical bulletin method for alachlor and pyriminobac-methyl were recently published. Because this method has some problems, such as many interfering chromatographic peaks for some residues in certain crops, time-consuming sample preparation, etc., we have developed an alternative method. In the bulletin method, pesticides are extracted with acetone, reextracted with ethyl acetate, partitioned with hexane-acetonitrile, cleaned up on a Florisil column, and quantitatively determined by gas chromatography with flame thermionic detector (GC-FTD). In the developed method, pesticides are extracted by supercritical fluid extraction and directly cleaned up with a trap column consisting of Extrelut and Florisil (acetone-n-hexane, 3 + 7, as the eluent) or Bond Elut SAX and PSA (acetone-n-hexane, 1 + f, as the eluent), The test solution was quantitatively determined by GC with mass spectrometry, Alachlor, pyriminobac-methyl, and 9 other chloracetanilide pesticides were studied. Average recoveries of spiked samples (0.1 ppm) were between 52 and 104% with the bulletin method and between 68 and 106% with the developed method. By using the Japanese bulletin method, 3 pesticides from Japanese radish could not be measured because of many interfering peaks on the GC-FTD chromatogram, even on selected-ion monitoring (SIM) chromatograms, On the other hand, by using the developed method, SIM chromatograms had fewer interfering peaks than did the Japanese bulletin method.